MTBE is a chemical compound that is manufactured for primary use in gasoline. MTBE, a colorless, flammable liquid with a turpentine-like odor, is highly water soluble, highly flammable, and extremely volatile. It is resistant to biodegradability in either aerobic or anaerobic conditions. MTBE is a common component in reformulated fuels developed to reduce smog and meet Clean Air Act goals and has been used in gasoline since 1979. The characteristics of MTBE are unlike those of other gasoline constituents and solvents. MTBE is highly soluble and migrates quickly with groundwater. Groundwater in equilibrium with gasoline containing 15 percent MTBE could contain as much as 9,600 ppm MTBE. It does not significantly adhere onto soil particles, and it does not appear to readily biodegrade in the environment.
MTBE is more difficult and more expensive to remove from water than other chemicals found in gasoline. Also, MTBE plumes can appear as discontinuous slugs. It moves more quickly through soil than most gasoline components, and its plumes tend to expand more rapidly. MTBE has been used in cold climates in the United States since 1979 as a de-icer. The Environmental Protection Agency (EPA) has tentatively classified MTBE as a possible human carcinogen, and in February 1991 the California EPA office of Environmental Health Hazard Assessment (OEHHA) established an interim action level of 35 ppb for MTBE. Depending on the state, regulatory requirements for MTBE range from 20 to 200 ppb.
MTBE is thought to get into surface waters such as lakes and reservoirs from the use of motorized watercraft. It may also travel into these waters in polluted runoff, or it may be deposited from the atmosphere by rainwater or other means. MTBE can get into groundwater from leaking underground fuel storage tank systems and leaking petroleum pipelines.
Available literature suggests that the treatment alternatives for removing MTBE from groundwater include pump and treat, air stripping, GAC absorption, and advanced oxidation processes.
Ethers under normal conditions are non-reactive and, in the case of MTBE, remain unchanged in soil and groundwater environments. However, oxidation by hydroxyl radical occurs readily with ethers. As long as the hydroxyl radical is in excess, this reaction will go to completion for all ethers, hydrocarbons or chlorinated solvents under controlled conditions.
It has long been known to ozonate water in order to oxidize pathogens and any other oxidizable organic or inorganic material that might be present in contaminated water. Ozone is a semistable gas formed of three oxygen atoms, instead of the two atoms that form oxygen gas. Ozone is most typically produced by an electrical arc discharged through air causing oxygen atoms to combine with an oxygen free radical that is formed. Ozone rapidly undergoes reaction to revert to more stable oxygen, releasing an oxygen free radical in the process. Two such free radicals can combine to form an oxygen molecule or the free radicals can oxidize an oxidizable substrate.
Ozone is fast emerging as the most efficient and ecologically sound oxidant to treat both organic and inorganic substances. Ozone has been used for water treatment for over 100 years, and is a preferred means of disinfecting potable waters. Many new applications of ozone are being evaluated.
A natural ingredient of the Earth's upper atmosphere, ozone (O.sub.3) is a three-atom allotrope of oxygen (O.sub.2) and exists in a gaseous form at ambient conditions. Ozone is such an aggressive oxidant, it is second only to fluorine in electronegative oxidation potential. However, unreacted ozone decomposes in a matter of hours to simple molecular oxygen and therefore cannot be stored. It must be produced on-site and destroyed by burning.